Running the Tank System before Adding Plants

In previous posts, we have gone through many steps to setup and insall every part of the tank. Now we can run the test for our system before adding plants. Did you know about this stage?

Empty tank with no plants, no fish

At this stage, you will be tempted to put in your plants, but wait at least 24 hours. This will allow you to check that the heater and filter are functioning properly; if there is a problem, it is easier to fix it now. At best you may need to replace or adjust the heater; at worst, the tank might leak. All these problems are easier to solve without plants in the tank. You will also give the water time to settle at the correct temperature. Plants, like fish, are tropical and will become chilled if they are plunged into water that is too cold. After a couple of hours, check the water temperature with your thermometer. Just dip it into the water to take a reading. There is no point in putting it in its final position as it will only be in the way when you begin to add the plants.

Thinking about the fish to add

Another decision to make at this point is which fish to keep. The number of fish you can keep in one tank depends on the surface area of the water. For tropical freshwater species, you need 75 sq cm (12 sq in) of surface area per 2.5 cm (1 in) of fish body length, not including the tail. This tank will hold a total of 60 cm/24 in (body length) of fish. You could start with four cherry barbs or White Cloud Mountain minnows, or a pair of platies. The total length of each of these groups of fish is about a quarter of the total allowable for this tank. Use this as a guide when adding more fish later. If you add a quarter of your fish every 10 days, you will have a fully stocked tank just as the filtration system has matured.

How the nitrogen cycle works

While we are waiting for the system to be ready for us to add the first plants, we should explore some natural chemical processes that take place within an aquarium. The most important of these is the circulation of nitrogen-containing compounds, commonly known as the nitrogen cycle. This natural process is the means by which dead and decaying waste products containing nitrogen are converted by bacteria from poisonous compounds, such as ammonia, into harmless substances, such as nitrates. These are then taken up by the plants. It will start happening in your tank as soon as you set it up and the filtration system will help it along. As the filtration system becomes colonized by helpful bacteria, it becomes more efficient. However, as soon as you add fish, there is a system overload and it takes a few days for the numbers of bacteria to build up to cope with the extra waste. This is why it is best to add a few fish at a time, not all of them at once. The first thing to happen is that bacteria break down the toxic ammonia excreted by fish and produced by decomposition. This is converted to less harmful, although still dangerous, nitrites, which are converted to much less harmful nitrates. In an ideal world, all the nitrates would be taken up by the plants, but in an aquarium, it is not that simple.

We usually overload our tanks with fish that produce too much waste for the plants to use. The result is high nitrate levels. The only way to remove these is by carrying out regular partial water changes.

• Ammonia is excreted by fish through the gills and in their waste products.
• Ammonia is converted to nitrites by bacteria in the filtration system.
• Nitrites are converted to nitrates by bacteria in the filtration system.
• Nitrates are taken up by the plants as a fertilizer.

Switching on the system

Water levels

Safety first

Make sure that all the equipment is properly installed (submersed to the correct levels and firmly attached) before switching on the power supply.

The water level in the tank can be 2.5 cm (1 in) or so below the final level but should cover the heater and filter to at least the recommended levels. You are then ready to switch on the system. For the time being, you can rest the condensation tray over the tank to prevent dust and debris from entering, and to deter any cats or children from tampering with it.

Oxygen levels

Oxygen (and other gasses) enter and leave the water at the surface and it is possible to increase oxygen levels by agitating the water surface using the bubbles from an airstone or the spray bar return from a power filter. Fish from different habitats need different oxygen levels. For example, fish from swift-flowing mountain streams need high levels, whereas those from swampy areas can stand much lower levels.

• Make sure the heater-thermostat is submerged.
• Any cloudiness in the water should be removed by the filtration system.
• Check that the filter system is working and adjust the direction and rate of flow if necessary.

Previous article: The Water and Adding the Aquarium Water
Next article: Planting the Aquarium